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northern section of the circle. Each bar protruded 2 ft., and would eventually be tied to the steel in the curved wall. A curved wall-More than half of the building is enclosed by a solid arc of concrete, lO in. thick and 8 ft. tall. This wall holds back the earth to the north, and supports a concrete ring beam that encircles the building, tying the structure together. Along the southern section, the weight of the ring beam is borne by the cast concrete columns (section drawing, previous page). We made the wall forms in 8-ft. by 8-ft. sec- tions, with %-in. plywood plates and 2x4 studs. After laying out the curved plates on the plywood, we cut them out with a jigsaw. As shown in the drawing at left, there is an inner form and an outer form. We lined the inside of both forms with Y2-in. plywood, which bent to the shape without any kerfs on the concave side. Once we had the forms in place, we applied another layer of Y2-in. plywood, which staggered the joints to tie the forms into a single unit. We then faced that with Ix4 #3 pine placed vertically to give a board-form impression (photo facing page, top). We left out a few rows of the Ix4s at the points directly opposite the columns. These would form shallow pilasters in the wall, continuing the rhythm of the columns around the wall. The only problem we had with the curved Two layers V2-in . plyWood Outer form Secton at snap tie Snap ties are steel rods that pass through concrete forms and secure the forms at a consistent spacing. As shown in the drawing, plastic cones ride on the rods, and bear against a flared lip on the rod and the inside surface of the forms. In the photo top right, the form on the right is in position, the one on the left still needs to be drilled for the rods to pass through it. On the outside of the forms (photo top left), steel wedges that bear on the walers draw the snap ties together. This form will be complete when a Sonotube column form is added atop the pedestal. A 10-in. wide section will be removed on the wall side of the tube to create an integral connection with the wall. we. Most roof solutions over drum-shaped bases are conical in section, but a cone-shaped roof didn't ring true for this building. A dome seemed like the right shape-its gentle rise culminating at the top in a round opening called an oculus (the Latin word for "eye"). [ thought we could find a way to build one, and with encouragement from our clients and our engineer, Mike Quinlan, [ went ahead and projected some costs. All along [ felt we could benefit by the regular geometry of the formwork and save labor costs as a result. This became even more apparent after running an estimate. Repetition became the key to making the project affordable. [f we could figure out how to make one section of the formwork, we could make jigs to speed the construction of the other sections. 66 Fine Homebuilding On the side of a hill-The site, in rural Douglas County, Kan., is a heavily wooded hillside with a dramatic view to the south. We decided to put the building near the top of the ridge, with its north wall nestled into the hillside and its south wall open to the view and the sun. As shown in the plan drawing on the previous page, the southern rim of the dome is supported by six columns, spaced about 5 ft. apart. After laying out a few test circles on the ground, we settled on a 26-ft. dia. space. Once our soils expert approved the site for our plans, we cut a road in, dug a doughnut-shaped trench for the grade beam and poured 25 yd. of concrete to support the walls and the dome. Along with the grade-beam steelwork, we included Y2-in. vertical rebar stubs on 16-in. centers along the forms was that the plywood kept remembering that it wanted to be flat. This caused us to lose the constant arc of the circle at the joints between form sections. We gradually smoothed out these kinks when we set the joists out from the center. The joists would eventually support the dome forms, and they also served as a platform for placing the concrete during the wall pour. Once we had the forms in the right place, we fastened their bottom plates to the grade beam with a powder-driven fastener in the center of each stud bay. Then we braced the entire assembly with tiebacks (angled 2x4 braces) at every other stud. We used snap ties to hold the IO-in. wall both together and apart (photos this page). Snap ties are steel rods that pass through concrete forms. They have ridges on them that separate a pair of plastic cones by a consistent distance (drawing, left). The cones bear against the inside of the forms, while the rods continue through the forms and past the studs and walers (the horizontal bracing) to be held fast by wedges. The flange on the end of the snap-tie rod is 8!4 in. from the cone, which allows enough room for a %-in. plywood form, a 2x4 stud, a 2x4 waler and the wedge. Snap ties come in various lengths so that you can build walls of different thicknesses. After the pour you snap off the rods flush with the wall, and the cones pop out. The ties are available from most concrete-product distributors, who will usually rent the wedges too. It's the simplest system available and easily modified for out-of-the-ordinary formwork. In our case, we used Ix4s for the walers, and made up the difference with wood spacers. The spacing of the snap ties is determined by the pressure of the concrete on the forms. It's better to over-design than to risk a form breaking during the pour. Our snap ties were on 16-in. Drawings: Elizabeth Eaton